In recent years, olefin metathesis reactions utilizing metathesis catalysts have become one of the most useful tools in organic chemistry. A wide variety of ruthenium metathesis catalysts possessing monodentate mixed ligand systems such as mixed N-heterocyclic carbene (NHC)/phosphine ligand systems are known and have been studied, a few examples of which are shown in Scheme 1. The benefits of ruthenium-metathesis catalysts possessing monodentate mixed NHC/phosphine ligand systems is well known in the art.

One particularly important olefin metathesis reaction is ring opening metathesis polymerization (ROMP). The molding of thermoset polymers by ROMP is a technologically and commercially important processing technique. In this technique, a liquid monomer (e.g., at least one cyclic olefin) and a polymerization catalyst (e.g., at least one metal carbene olefin metathesis catalyst) are mixed to form a ROMP composition, and the ROMP composition is poured, cast or injected into a mold. The polymerization proceeds and upon completion the molded part is removed from the mold for any optional post cure processing that is required. The ROMP composition may optionally contain added modifiers, fillers, additives, reinforcements, pigments, etc.
Unfortunately little work involving ruthenium metathesis catalysts possessing monodentate mixed ligand systems other than mixed NHC/phosphine ligand systems has been disclosed. Furthermore, many of the previously known ruthenium metathesis catalysts possessing mixed NHC/phosphine ligand systems possess characteristics which in some instances limit their use in certain applications and olefin metathesis reactions. Therefore, there is an ongoing need for metal carbene olefin metathesis catalysts, particularly ruthenium metathesis catalysts containing monodentate mixed ligand systems with improved characteristics which will further enable their use in a wider array of applications and olefin metathesis reactions.